A conventional camera capable of obtaining planar image information and stereoscopic image information is, for example, a 3D camera described in Patent Document 1 specified below.
FIG. 10 is an external view of a conventional 3D camera 910 including two camera heads, i.e., a fixed head 915 and a movable head 916, and FIG. 11 is a block structural diagram of a main part of the 3D camera 910.
The fixed head 915 is fixed to a main body of the 3D camera 910, whereas the movable head 916 can be slid and thus moved by operating a moving button 912. In FIG. 10, the movable head 916 is shown in the state of having been moved to an outermost position in a movable range thereof. In FIG. 11, reference numeral 916 represents the movable head in the state of having been moved to the outermost position in the movable range thereof, and reference numeral 916′ represents the movable head in the state of having been moved to an innermost position in the movable range thereof.
The fixed head 915 and the movable head 916 respectively include a fixed head lens 917 and a movable head lens 918. The fixed head lens 917 and the movable head lens 918 are respectively zoomed in or out by a zoom motor 926 and a zoom motor 929 described later.
The fixed head 915 and the movable head 916 respectively have an optical axis 937 and an optical axis 938 which are parallel to each other regardless of a gap therebetween. The fixed head 915 and the movable head 916 each include a charge coupled device (CCD) sensor, which is an image pickup element. The fixed head 915 and the movable head 916 are substantially identical with each other, and located in a common plane which is vertical to the optical axis 937 and the optical axis 938.
The movable head 916 is structured to be slidable and thus movable in the state where the optical axis 937 and the optical axis 938 are kept parallel to each other and both of the movable head 916 and the fixed head 915 are located in a plane vertical to these two optical axes.
The fixed head 915 and the movable head 916 are controllable by a user. For example, the user may press the moving button 912 located in an upper part of the movable head 916 with his/her finger to slide and thus mechanically move the movable head 916. Alternatively, the user may rotate a dial 913 connected to the movable head 916 via a worm gear to adjust the gap between the fixed head 915 and the movable head 916. In another example, the user may rotate a motor with an electronically controllable button switch or the like, such as a rightward moving button and a leftward moving button, to move the movable head 916.
The position of the movable head 916 is measured by a position encoder 925 and is input to a vision feedback unit 932, which is a circuit for determining a field of view and a focal distance of each of the fixed head lens 917 and the movable head lens 918. The position encoder 925 includes a linear potentiometer for detecting the position of the movable head 916. In another example, the movable head 916 may be moved by a stepper motor and the position thereof may be measured by counting the number of steps of the motor.
The vision feedback unit 932 controls a zoom control unit 924 in order to adjust the focal distance of each of the fixed head lens 917 and the movable head lens 918. The zoom control unit 924 controls the zoom motor 926 and the zoom motor 929. At this point, the focal distances are controlled to maintain the same value with each other.
The vision feedback unit 932 also receives detailed information on a display unit 933 for displaying a captured image from a display unit element determination unit 930. This information is, for example, a preset value indicating a screen size or a prescribed observing distance of the display unit 933. Alternatively, the user may input appropriate data as such information.
The vision feedback unit 932 further receives subject depth information from a subject depth determination unit 931. The subject depth determination unit 931, in a simplest structure thereof, may merely set an apocenter to infinity and set a pericenter to a minimum focal distance of the camera. In a more advanced example, for instance, where the camera is of an autofocus type, one or more depth range limit values may be measured by an autofocus sensor. In order to maximize the flexibility, the auto focus sensor is directed to the closest point or the farthest point in the image to be captured and thus accurately measured distance data is supplied to the vision feedback unit 932.
In addition to controlling the zoom motor 926 and the zoom motor 929 to adjust the focal distance of each of the fixed head lens 917 and the movable head lens 918, the zoom control unit 924 supplies the vision feedback unit 932 with information indicating whether or not the camera of the fixed head 915 and the camera of the movable head 916 operate within tolerable conditions. For example, when a maximum parallax condition is exceeded, the zoom control unit 924 notifies the vision feedback unit 932 that an image which will be captured with the current camera setting is inappropriate. The vision feedback unit 932 notifies the user of this through information which is displayed on the display unit 933. Similarly, when the depth of a captured image is too small, the zoom control unit 924 may provide a display indicating that good 3D perception will not be obtained.
An image captured by the image pickup element of each of the fixed head 915 and the movable head 916 is sent to an image processing unit 934. The image processing unit 934 processes the captured image based on data sent from the zoom control unit 924 or the vision feedback unit 932, and displays the resultant image on the display unit 933.
Alternatively, a post-processing or pre-processing image may be stored on a fixed or detachable memory 935. In the case of the detachable memory 935, the memory 935 may be transferred to another device to transfer the image to the another device, for example, a computer or a three-dimensional projector. In this manner, the image may be subjected to other types of processing or stereoscopic display.
In the case where, for example, the 3D camera 910 includes a communication unit (not shown), the communication unit may be used to transfer the image to an other device, for example, a computer or a three-dimensional projector. In this manner, the image may be subjected to other types of processing or stereoscopic display.
The vision feedback unit 932 receives information indicating the position of the movable head 916 and the gap between the fixed head 915 and the movable head 916 from the position encoder 925. The vision feedback unit 932 also receives information indicating the focal distance of each of the lens of the fixed head 915 and the lens of the movable head 916 from the zoom control unit 924, and determines the field of view of the camera based on both of the information regarding the focal distances and the information regarding the gap between the fixed head 915 and the movable head 916. For example, where the fixed head 915 and the movable head 916 have a maximum gap therebetween, the focal distances of the fixed head lens 917 and the movable head lens 918 are adjusted such that the camera has the widest field of view. By contrast, where the gap between the fixed head 915 and the movable head 916 is set to be minimum, the fixed head lens 917 and the movable head lens 918 are controlled such that the camera has the narrowest field of view within a usable range.
conventional liquid lens which uses a liquid as a lens material and is capable of changing a focal distance thereof by an electronic control is, for example, a liquid microlens described in Patent Document 2 specified below.
FIG. 12 is a cross-sectional view of such a conventional liquid microlens 960.
The liquid microlens 960 includes a droplet 962 formed of a transparent liquid. The droplet 962 has a diameter of several micrometers to several millimeters. The droplet 962 is located on a transparent substrate 964. The transparent substrate 964 is hydrophobic or has a hydrophobic coating layer. Accordingly, the droplet 962 has a very strong interface tension to the transparent substrate 964, and if being left without being processed, tends to be shaped spherical as a result of being “repelled” by the transparent substrate 964. However, by an electromagnetic control of applying a predetermined voltage between the droplet 962 and the transparent substrate 964, the interface tension of the droplet 962 to the transparent substrate 964 can be weakened by an electron wettability phenomenon. As a result, a lens in which an angle of an end of the droplet 962 with respect to the transparent substrate 964 is θ can be formed.
The transparent liquid which forms the droplet 962 and the transparent substrate 964 are transparent with respect to light having a wavelength in a certain range including visual light rays.
Light rays 966, which are incident on the liquid microlens 960 and are vertical to the transparent substrate 964 and parallel to each other, pass the liquid microlens 960 and are collected to a focal point 968 which is distance f away from the contact face of the droplet 962 and the transparent substrate 964.
Contact angle “θ” between the droplet 962 and the transparent substrate 964 is determined by interface tension “Y” mentioned below (usually measured with millinewton per meter (mN/m)).
In the liquid microlens 960, the angle θ is represented by expression 1 where YS-V is the interface tension between the transparent substrate 964 and air (or a gas or another fluid) enclosing the transparent substrate 964, YL-V is the interface tension between the droplet 962 and air (or a gas or another fluid) enclosing the droplet 962, and YS-L is the interface tension between the transparent substrate 964 and the droplet 962.
                              cos          ⁡                      (            θ            )                          =                                            Y                              S                -                V                                      -                          Y                              S                -                L                                                          Y                          L              -              V                                                          [                  Expression          ⁢                                          ⁢          1                ]            
Where the volume of the droplet 962 is V, the radius of curvature “R” of the curved surface of the droplet 962 is represented by expression 2.
                              R          3                =                              3            ·            V                                                              π                ⁡                                  (                                      1                    -                                          cos                      ⁢                                                                                          ⁢                      θ                                                        )                                            ⁢                              (                                  2                  -                                                            cos                      2                                        ⁢                    θ                                    -                                      cos                    ⁢                                                                                  ⁢                    θ                                                  )                                      ⁢                                                                                    [                  Expression          ⁢                                          ⁢          2                ]            
The focal distance f of the liquid microlens 960 is the function of the radius R and the refractive index “n”.
Where nL is the refractive index of the droplet 962 and nV is the refractive index of air (or a gas or another fluid) enclosing the droplet 962, the focal distance f is represented by expression 3.
                    f        =                  R                                    n              L                        -                          n              V                                                          [                  Expression          ⁢                                          ⁢          3                ]            
Since a top surface and a bottom surface of the transparent substrate 964 are parallel to each other, refractive index thereof is not an issue. Where the volume V of the droplet 962, the refractive index nL of the droplet 962, and the refractive index nV of the air enclosing the droplet 962 are assumed to be constant (usually, V, nL and nV are considered to be constant), the focal distance of the liquid microlens 960 is the function of only the contact angle θ.
FIG. 13 is a schematic view of an electronic wettability phenomenon. By this electronic wettability phenomenon, contact angle θ1-θ2 between the droplet 962, which is a conductive fluid, and a dielectric insulating layer 974 having a dielectric constant of “εγ” and a thickness of “d” can be reversibly changed. Therefore, a liquid microlens, the focal distance of which is reversibly changeable, can be provided.
As shown in FIG. 13, a metal electrode 976 is located below the dielectric insulating layer 974, and is insulated by the dielectric insulating layer 974 from a droplet 972, which is a conductive fluid. The droplet 972 is, for example, a small water drop, and the dielectric insulating layer 974 is, for example, a thin film or a thin plate formed of Teflon (registered trademark)/Parylene as a material.
Without any voltage difference between the droplet 972 and the metal electrode 976, the droplet 972 maintains a shape defined by the volume of the droplet 972 and the contact angle θ1. The contact angle θ1 is determined by the interface tension, as described above.
As described above, since the dielectric insulating layer 974 is hydrophobic, the droplet 972 tends to be shaped spherical as a result of being “repelled” by the transparent substrate 974.
The shape of a droplet 978 represented by the dashed line shows the following state. As a result of a voltage V being applied between the metal electrode 976 and the droplet 972, an electronic wettability phenomenon occurs, and the hydrophobicity of the dielectric insulating layer 974 with respect to the droplet 972 is weakened (the hydrophilicity thereof is intensified); and therefore, the droplet 972 is uniformly diffused with respect to the dielectric insulating layer 974. The voltage V at this point is in the range of several volts to several hundred volts, and the polarity is irrelevant. By applying the voltage V between the metal electrode 976 and the droplet 972, the contact angle is decreased from θ1 to θ2. A diffusion amount determined by the difference between θ1 and θ2 is the function of the voltage V, and the contact angle θ2 is represented by expression 4.
                              cos          ⁢                                          ⁢                      θ            ⁡                          (              V              )                                      =                              cos            ⁢                                                  ⁢                          θ              ⁡                              (                                  V                  =                  0                                )                                              +                                                                      ɛ                  0                                ⁢                                  ɛ                  γ                                                            2                ⁢                d                ⁢                                                                  ⁢                                  Y                                      L                    -                    V                                                                        ⁢                          V              2                                                          [                  Expression          ⁢                                          ⁢          4                ]            
In expression 4, θ (V=0) is the contact angle between the dielectric insulating layer 974 and the droplet 972 when no voltage is applied between the droplet 972 and the metal electrode 976. YL-V is the interface tension between the droplet 972 and air (or a gas or another fluid) enclosing the droplet 972. εγ is the dielectric constant of the insulating layer. ε0 is the permeability of vacuum, i.e., 8.85×10−12 F/m.
Utilizing such an electronic wettability phenomenon, a liquid microlens, the focal distance of which is reversibly changeable, can be formed.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2001-142166    Patent Document 2: Japanese Laid-Open Patent Publication No. 2003-050303